Mast materials and Specifications

  • 02 Jun 2013 22:28
    Reply # 1307605 on 1307257
    Gary King wrote:Well, the plot is thickens with Lexia's mast.  5" is pretty wimpy, but says something if it lasted for several decades (?). I feel much better about mine..

    Lexia's main mast is 5 inches but the foremast was I understand 3 1/2 inches (subject to confirmation by measuring tomorrow!).  The break at the deck level shows it to have been sleeved.  The total length of the foremast is 30 feet. 

    The recommendation from Alan Boswell, the designer, via Robin Blain ,the last link with the manufacturer, is to replace the foremast with 5 inch outide diameter and 1/4 inch wall thickness grade 6082 T6 anodised.  Apparently Alan Boswell then quoted a resultant safety factor of 2.72.

    However, Robin also suggested the bottom half or so in 5" with the top  half in 4", although I am not sure if that would result in a step between thicknesses which would result in some drag against the batten parrels on reefing or stowing. 

    I am simply reporting here, not necessarily claiming to  understand or have a view.  However, I may need to take a view shortly. 

    I presume that both masts are original from 1978.  That is certainly the view of Robin Blain .

    I should now record that overnight on Wed / Thu I had reduced sail.  It was rough, steep Channel chop, as there had been some days of heavy weather from the SW and the tides were springs. 'I slept in 10 minute stretches.  We sailed SW on a beam reach at about 4 knots.  At dawn the wind dropped and we wallowed at around half a knot.  If I had been just cruising I would probably have thought fine, let's wallow whilst I get some rest.  Alas, I thought that I should get some sail on and as it was pretty much dead calm I put both sails up fully.  I went below and set my timer for 15 mins.  As I woke up I noted that we were sailing much faster.  Just as I was getting up to look out the foremast went over the side, breaking at the deck. 

    So, my fault I think.  A bad desision, perhaps made because I was tired and was very sea sick. 

    Or maybe it was a failure waiting to happen. 

    Uninsured as I was technically racing.  Salt in the wounds. 

    Interestingly, Denis Sidebotham's 5" alloy mainmast on Janvier Aquilla failed at deck level two years ago in Plymouth Sound.  That was probably a similar vintage. It wasn't very rough or strong wind. In his case the inshore lifeboat came out and rescued his sail, yard, boom and battens.  The mast was let go in 50 feet.  Dennis says that I can have the mast if I can find and retrieve it.  I think that it is a very long shot ... !


    Last modified: 02 Jun 2013 22:52 | Anonymous member
  • 02 Jun 2013 21:30
    Reply # 1307580 on 1306051
    Epoxy should best not be coated in a dark colour snd it should be protected from UV radiation.
    There are lots of types of epoxy which all have their use. To get epoxy to stand higher temperatures usually it has to be baked. That means you give it a heat treatment in order to raise the temperature it turns soft. This baking process is specified by the producer of the stuff. Baked at high (specified ) temps it will have best quality and highest temperature tolerance.
    The newer types I used for masts need lower than before to reach good quality and temp tolerance. Things are developing everywhere.

  • 02 Jun 2013 14:50
    Reply # 1307404 on 1306051
    Deleted user
    I think for a timber mast (the laminated epoxied up kind - not a grown tree) the solution is glass sheaved and painted white to keep UV out and keep it cool, like the original Badger masts, which AFAIK are still going strong after 30 years. Thats how the tops of Ashiki's hybrid masts have been finished.

    Epoxy is so damn delicate, goes kaput fast if it isnt coated properly. Even coated in a dark colour, cracks develop within a year. I think there's some threshold temperature where epoxy starts to fail, something like 80˚C, not too sure.
    Last modified: 02 Jun 2013 15:03 | Deleted user
  • 02 Jun 2013 12:15
    Reply # 1307335 on 1306051
    Arne, I like the sound of those dug-out spruce masts.  Not sure if I could get enough good quality spruce here but I'd certainly consider it if I had to replace my mast, which I hope not to.  David Tyler said he thinks it will last my lifetime, as far as fatigue goes.  Capsize (I want to go offshore voyaging again soon) or corrosion may be another matter, though the latter seems to be under control.  Your hybrid mast looks good and Annie has given hers a good test without any weaknesses showing up so far, so perhaps that would be another option for me.

    Apart from Galway Blazer, has anybody else given thought to an inbuilt jury rig system?  GB's bipole jury rig was ingenious but best suited to long light boats with lots of fore and aft deck space.  It would be hard to fit such a system on a short fat boat like Arion. (With apologies to Arion - As the famous Jazz song goes, "Don't call me fat, honey.  I am built for comfort, not for speed.")
  • 02 Jun 2013 07:56
    Reply # 1307261 on 1306051
    Anonymous member (Administrator)

                                                                       Stavanger, Sunday

    Graham, I surely like the dug-out spruce masts that I have had. Johanna’s 250mm mast is now 11 years and in good conditions, but I would still beef up the glass sheathing to 2-3 layers next time i build one - if there will be a next time. The sheathing of Malena’s mast lasted for only 12-14 years and now needs partial replacement. This was only varnished (2-pot Polyurethane) and I suspect that this has given the epoxy less protection from the sun than the paint on Johanna’s mast does.

    The strong argument for the hybrid mast is that it is so quick to make. The dug-out spruce mast called for quite some work to build (but not super accuracy) and also long waiting for the log to cure. Building from staves sounds like a BIG job and calls for high quality at every stage. In comparison the recent construction of my new hybrid mast was a walk in the park.

    Cheers, Arne

    Last modified: 02 Jun 2013 08:03 | Anonymous member (Administrator)
  • 02 Jun 2013 07:25
    Reply # 1307257 on 1306051
    Deleted user
    Well, the plot is thickens with Lexia's mast.  5" is pretty wimpy, but says something if it lasted for several decades (?). I feel much better about mine..
    Last modified: 02 Jun 2013 14:38 | Deleted user
  • 02 Jun 2013 04:13
    Reply # 1307204 on 1306051
    My junk-rigged sistership, Minke, has a solid timber mast, laminated from 2 inch (50mm) oregon planks.  It is 10 inches (250mm) at the partners, is unsheathed and oiled regularly.  It is still perfect after 20 years.  I'd be tempted to build a timber mast next time, though probably built like Gary Pick's (see his article in the newsletter).  I don't want to go up my mast to oil it, and if I had a 250mm dia I would have to rebuild the partners..  I would HEAVILY sheath it in epoxy and glass.  Lovely stuff, wood.

    I must give a nod to Paul's hot dip galvanised steel masts.  They will never fatigue and will not need a lot of maintenance.  I have a friend, fellow JRA member Terry Pentford, who has been cruising Asia with steel masts in his junk schooner, Si Hai, for some years.  He had to replace his original hoop pine masts which rotted.  The reason they rotted was because they were just sealed with epoxy resin (not sheathed in glass), which cracked and trapped moisture.  Terry is convinced that if he'd just oiled them he's still be using them.

    Another reason for liking timber is that my alloy mast is horrible noisy when the battens and parrels rub back and forth.  Ditto for steel, I presume.  Anyway, it's alloy I've got, so, until it falls down...I guess we are pioneers.  It's nice to be a pioneer.  Makes a change from hiding under the table...

  • 02 Jun 2013 04:02
    Reply # 1307202 on 1306725
    Deleted user
    Mark Thomasson wrote:
    That said, the straight tube with a tapered top has a lot going for it, and would be my choice for economy (unless my lottery ticket comes up, then it is carbon fibre).  I would strengthen the lower 1/3 with an outer sleeve.  Has anyone tried options for the tapered top, other than wood?  Aluminium flagpole, fibreglass flagpole.  Or perhaps even using the lighter aluminium tube for the top and timber for the bottom?  (I know I should look at the mast data base, but it is not to hand on this computer,  and I cannot find it in the website). 

    Hello Mark,

    I'm using two HAPCO light poles (same kind as for utility / street lights) which were specified by my naval architect for use with my Junk Rig.  They are standard items in the US, about $2000 USD each for a 40 foot section, are smoothly tapered, re-tempered after welding for uniformity, and the bases are easily cut off for stepping and make fine collars at the step.

    I have put absolutely zero sail time on them yet, though, but the rig is up so I know they fit.  You'll have to either order them with a painted finish or hand-sand them - the unpainted default finish is quite rough as I found out to my chagrin.

    For those of you curious, the wall thickness is in excess of 0.25 inches (roughly 6mm+) the entire way up.  The 40' mast weighed just shy of 285 lbs (from memory, I could be wrong).

  • 02 Jun 2013 03:07
    Reply # 1307179 on 1306750
    Gary King wrote:
    All this makes a great advert for timber masts..

    Indeed it does, and I would have chosen one myself, except for the fact that it isn't easy to buy suitable (and affordable) wood in NZ.
  • 01 Jun 2013 12:01
    Reply # 1306750 on 1306051
    Deleted user
    Heres a definition I found somewhere:

    "The effect on metal of repeated cycles of stress. The insidious feature of fatigue failure is that there is no obvious warning, a crack forms without appreciable deformation of structure making it difficult to detect the presence of growing cracks. Fractures usually start from small nicks or scratches or fillets which cause a localised concentration of stress. Failure can be influenced by a number of factors including size, shape and design of the component, condition of the surface or operating environment."

    Beefing up the size would slow the fatigue process down, in the bottom half of the mast that is.

    All this makes a great advert for timber masts..
       " ...there is nothing - absolutely nothing - half so much worth doing as simply messing about in junk-rigged boats" 
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